DESTABILIZATION OF PH HOMEOSTASIS IN FROG NERVE-FIBERS CAUSED BY HYPERACTIVATION OF NA+-CHANNELS, BLOCKADE OF NA-K+ PUMP AND NA+/H+ EXCHANGERстатья

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[1] Destabilization of ph homeostasis in frog nerve-fibers caused by hyperactivation of na+-channels, blockade of na-k+ pump and na+/h+ exchanger / O. VALKINA, O. VERGUN, V. TUROVETSKY, B. KHODOROV // Biologicheskie Membrany. — 1995. — Vol. 12, no. 4. — P. 360–373. Cytoplasmic pH (pH(i)) in frog nerve fibres (sciatic nerve and its thin bundles) was measured using fluorescein diacetate. Under control conditions, repetitive stimulation (50 Hz) induced only a slight (by 0,06 unit) decreace in pH(i). Veratridines (VER) treatment of the nerve considerably enhanced the stimulus-evoked (SE) intracellular acidification, which became irreversible after blockade of the Na+/K+ pump with ouabain. The inhibition of the lactic acid production by iodacetamide as well as the blockade of Cl- influx by SITS did not prevent or attenuate the VER and SE intracellular acidification. Blocking of the Na+/H+ exchange by EIPA enhanced the SE intracellular acidification. In the presence of EIPA, post-stimulatory recovery of pH(i) was replaced by post-stimulatory cytoplasmic acidification. Lowering of the external pH (pH(o)) to 6.5 enhances, whereas the elevation of pH(o) up to 9.0 considerably diminished the SE intracellular acidification. The hypothesis is put forward that the SE intracellular acidosis results from the excessive influx of H+ and Na+ into the fibre via activated Na+ channels: internal Na+ suppresses the Na+/H+ exchange which potentiates pH(i) decrease caused by H+ influx.

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